Electrode for sparking plugs



Marc 21, 1944. J, HASTON ETAL 2,344,597'I ELECTRODE FOR SPARKING PLUGS Filed March 9, 1942 I Ckaslon czml K616. Per-twee Patented Mar. 21, 1944 ELECTRODE FOR SPARRING PLUGS Jack Chambers Chaston and Kenneth Stuart Guy Pertwee, Harrow, England, assignors to Johnson, Matthey & Co. Limited, London, England,

a British company Application March 9, 1942, Serial No. 434,004 In Great Britain March 18, 1941 This invention relates to-electrodes for sparking plugs, constructed of platinum alloys having improved characteristics.

It has already been proposed to use platinum, iridium, or ruthenium, either alone or alloyed with each other or with osmium or tungsten for electrodes of the said kind. The electrodes thus obtained have a longer life than the easily oxidised base metal electrodes previously used and many of them withstand corrosion by the lead compounds normally added to high-grade motor spirit to prevent knocking. Many of the alloys, however, are extremely diillcult to fabricate to the form of wire and are liable to have hidden flaws and internal defects. Furthermore, some of the alloys are relatively soft and the electrodes are liable to be readily deflected when at high temperatures. This latter defect is extremely serious, since if the alloys lose their stiffness at high temperatures the gap between the electrodes may alter in length and injuriously affect the performance of the engine in plugs are used.

We have now found that these difficulties can be overcome by the use of platinum alloyed with from 0.5% up to of molybdenum for the sparking plug electrodes. Contrary to expectawhich the tion, we find that these molybdenum-platinum alloys do not lose molybdenum when heated in air but remain bright and untarnished. The stability of the molybdenum-platinum alloys on heating is remarkable, in view of the volatile' nature of the oxide of molybdenum, M003. In one test, wires 0.020 inch in diameter were heated for 24 hours in freely circulating air to.1100 C. by the passage'of an electric current. A small amount of volatilisation occurred during this treatment, as with all platinum metals; but there were no indications of any preferential loss of molybdenum; the composition of the wires remained unchanged as far as could be detected by chemical analysis. The total loss of weight of the wires is shown in the following table:

Per cent total gloss ol weight alter 24 hours 3 Claims. (Cl. 123-169) although the molybdenum-platinum alloys containing from 0.5 to 10% molybdenum are very hard, they are readily fabricated by forging, rolling and wire drawing. These molybdenumplatinum alloys are, unexpected, nearly twice as hard as the corresponding tungsten-platinum alloys and are very much easier to work. The hardness of the alloys, measured after annealing at 1400 C. is as follows:

Per cent Vickers pyramid rdness No.

In contrast, the Vickers hardness of the alloy of Pt with 20% Ir, when fully annealed, is 180; and the Vickers hardness of the alloy of Pt with 4% W, which has recently been proposed as a sparking plug alloy, is only about 140,

Within the range of 0.5 to 10% molybdenum, the preferred range from considerations of both hardness and workability is 2 to 6%. As an of illustration, a conventional type of sparking plug is shown in the accompanying drawing in part section.

In the drawing the body part d has a screw threaded portion adapted to'be screwed into a hole inthe engine cylinder. Within the hollow body part d is an insulated central stem a to which is secured an electrode 12 made from a short length of wire of substantially uniform diameter. The complementary electrode 0 is mounted on the body part d and consists of another short length of wire. In applying the present invention to this sparking plug, the wire electrodes 7) and c are made from a molybdenumplatinum alloy as hereinbefore specified.

meme

2. m electrode for a sparking plug consisting of a platinum-molybdenum alloy containing molybdenum within the range 2-6%, the balance being platinum.

' 3. An electrode for e. sparking plug consisting of e, plntinummolybdenum alloy containing 4% molybdenum and 96% platinum.

JAG m CHASTON. 1 1:; SJG. PERTWEE. 

